A conventional pulverized-coal burner comprises a housing provided with an inlet pipe connection for steam supply; a central tube with ducts for supplying a fuel gas and an oxygen-containing gas, and with a combustion chamber provided at the end of said central tube; a pipe section arranged between the housing and the central tube; coiled tubular elements for supplying pulverized coal which are arranged helically around the central tube; and ducts for supplying an oxidizing agent which are connected to an inlet manifold and to an outlet manifold, the latter being provided with a number of discharge nozzles (Application DD, No. F 23 D/266 958).
However, the burner described above has the following disadvantages: a low reliability in operation and a poor quality of the gas produced. The low reliability of this conventional pulverized-coal burner is due to the following: the discharge nozzles for the supply of the oxidizing agent are provided on the outlet manifold and are arranged between the housing and the jacket section, whereas the openings of the discharge nozzles are on a level with the discharge area of the housing. Since there is a continuous circulation of steam in the space between the housing and the jacket section, and since the ducts for the supply of the oxidizing agent are purged with steam prior to start-up, the discharge nozzles have a high temperature prior to the oxygen supply (normally 300.degree. to 400.degree. C.) which is due to the high temperature of the steam. During oxygen supply and the ignition of the pulverized coal the discharge nozzles are subjected to a further heating due to the radiation of the flame. The metal of the discharge nozzles is oxidized by the jet of oxidizing agent and even ignites if technical oxygen is used as an oxidizing agent.
The poor quality of the gas obtained from the gasification process is due to the fact that the flow of pulverized coal from the swirl chamber into the reaction chamber is nonuniform. The pulverized coal is supplied in a dense phase from a feed bin via several ducts to the pulverized-coal burner. In the swirl chamber the weak pulsations of the pulverized-coal streams from the individual ducts superimpose each other and are intensified, thus creating a strongly pulsating pulverized-coal flow at the burner port. Consequently, within a specified period of time a constant flow of oxidizing agent mixes with varying amounts of pulverized coal. This has an adverse effect on the quality of the gas produced. With a reduction of the throughput of pulverized coal the percentages of carbon monoxide and hydrogen in the producer gas decrease, and an increase of the pulverized-coal throughput hampers the gasification process: the amounts of carbon monoxide and hydrogen produced are too small, and the gas contains substantial quantities of unreacted carbon.
With respect to design and effects to be attained a pulverized-coal burner characterized by the features summarized below is quite similar to the proposed invention. A housing provided with an inlet pipe connection for the supply of a mixture of steam and an oxidizing agent comprises a pipe section and a central tube which are arranged coaxially to form annular spaces. The central tube is provided with ducts for supplying a fuel gas and an oxygen-containing gas, with the outlets of these ducts opening into a combustion chamber to produce a pilot flame. Coiled tubular elements for supplying pulverized coal are arranged helically around the central tube and open into a swirl chamber which is bounded by a transverse partition between the central tube and the pipe section and by the lower parts of the pipe section and the central tube. The space between the housing and the pipe section is closed by a bottom plate which is provided with a water-cooled jacket as are the housing and the pipe section. This bottom plate is provided with discharge nozzles for the supply of a mixture of steam and an oxidizing agent which pass through the water-cooled jacket and open to the outside (Application DD, No. F 23 D/276 285).
This burner has disadvantages as well, i.e. a low reliability in operation and a poor quality of the gas produced. The low reliability of this type of pulverized-coal burner is due to the fact that the discharge nozzles for oxidizing agent supply which are provided in the bottom plate and pass through the water-cooled jacket are cooled insufficiently. The cooling water flows laterally around the nozzles thereby forming a stagnation zone on their opposite side, and cooling effects are considerably reduced in this area; the coolant may even boil in some places and the water-cooled jacket may burn through around the nozzles. Another reason for the low reliability of the conventional pulverized-coal burner is that the cooling jacket is in no way protected against flame action and that the metal is exposed to the detrimental effects of large heat flows (300-800.multidot.10.sup.3 kcal/m.sup.2 .multidot.h).
The poor quality of the gas produced is due to the fact that the flow of pulverized coal into the reaction chamber is non-uniform. If a single stream of pulverized coal is supplied to the swirl chamber in a dense phase, it is not possible to attain a uniform distribution of the pulverized coal in the outlet area of the chamber since the flow does not fully rotate in the chamber. Thus, an area of an increased concentration of pulverized coal and an area of a reduced concentration of pulverized coal are formed in the reaction chamber, and more particularly close to the burner port. Since the oxidizing agent is supplied to the reaction chamber in a uniform flow, such an unfavorable distribution of the pulverized coal considerably impairs the quality of the gas obtained.
In the process of dense-phase conveying and feeding of the pulverized coal into the swirl chamber via several ducts the following phenomenon is observed: in the chamber the weak pulsations of the pulverized-coal streams from the individual ducts superimpose each other. Consequently, the entire stream of pulverized coal begins to pulsate strongly, the flow into the reaction chamber is nonuniform and this, in turn, has an adverse effect on the quality of the gas obtained form the gasification process.